Earthquake response of tall reinforced concrete chimneys

Codes of practice around the world provide conservative
guidelines for the aseismic design of tall reinforced
concrete chimneys in the belief that such structures
would behave in a brittle manner when subject to severe
earthquake excitation. This has resulted in reinforced
concrete chimneys being prohibitively expensive in
regions of high seismicity. It has recently been established
from an experimental program that reinforced
concrete chimneys respond in a moderately ductile manner
under severe reverse cycle loading through yielding
of the reinforcement in tension provided that the sections
possess a reasonable curvature capacity [1].
The results from the experimental program have been
used to develop a non linear dynamic procedure for evaluating
the inelastic response of tall reinforced concrete
chimney structures described in this paper. The procedure,
which incorporates a cantilever model with discrete
plastic hinges is used to study the response of ten
chimneys, ranging in height from 115 m to 301 m, to
severe earthquake excitation. In particular, the response
behaviour and the failure modes of these chimneys associated
with an ensemble of earthquake ground motions
is described.
Based on the non linear dynamic study, a series of
code design recommendations have been prepared which
encourage the development of ductile behaviour to dissipate
the seismic energy and prevent the formation of
brittle failure modes. These recommendations have been
incorporated into the 2001 CICIND code [2] for the
design of reinforced concrete chimneys and result in
cheaper chimneys which perform better under earthquake
excitation (CICIND is a French acronym for International
Committee on Industrial chimneys). The justification
for the selection of a structural response factor
of R=2 which reduces the seismic design forces and satisfies
both the serviceability and structural stability limit
states is presented using a deterministic approach.
Finally, a comparison of the cost and performance of a
245 m tall chimney designed to the proposed seismic
code provisions is made with the 1998 ACI 307, 1998
CICIND, 1996 EC8-3 and 1997 UBC codes of practice
[2–5].
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